Polyelectrolyte nanocapsule probe for the determination of imidacloprid in agricultural food samples

Figures & data

Table 1. Comparison of the proposed assay with reported methods for imidacloprid detection.

Method	linear range (ng mL^−1)	IC50 of target (ng mL^−1)	LOD of target (ng mL^−1)	Reference
ELISA	–^a	35.00	–	Li and Li (2000)
ELISA	5.00–125.00	17.30	–	Lee, Ahn, Park, Kang, and Hammock (2001)
ELISA	1.30–50.00	3.30	–	Wanatabe et al. (2001)
ELISA	1.00–39.00	8.00	0.50	Watanabe et al. (2004)
ELISA	–	995.40	30.00	Li et al. (2007)
ELISA	–	6.50	0.20	Ma et al. (2009)
ELISA	–	14.80	0.11	Girotti, Maiolini, Ghini, Eremin, and Ma Es (2010)
ELISA	–	1.20–3.00	0.03–0.16	Wang, Wang, Yang, Wang, and Deng (2012)
GICA	–	–	10.00	Fang et al. (2015)
Selection of phage-displayed peptides based assay	8.00–906.00	96.00	2.30	Liu et al. (2015)
Nanoplasmonic biochips	–	–	0.20	Lee et al. (2016)
ELISA	0.10–8.10	0.93	0.05	Commercial kit
Proposed assay	0.02–0.84	0.11	0.01	This study

^aNot mentioned.

Figure 1. Schematic of preparation of nanocapsule probe and the probe-based assay procedure. (A) Synthesis illustration of nanocapsule probe and (B) protocol of the enhanced assay. (a) Coating antigen (0.25 μg mL⁻¹, 100 µL) was added to 96-well plate and incubated 2 h at 37°C. (b) Imidacloprid (100 µL) and mAb (0.125 μg mL⁻¹, 100 µL) were added and incubated 1 h at 37°C. (c) The probe (100 µL) was added and incubated 1 h at 37°C. (d) Substrate solution (100 µL) was added and incubated 15 min at 37°C.

Figure 2. Synthesis confirmation of nanocapsule probe. (A) TEM images of the AuNPs (a) and the synthesized nanocapsule probe (b). (B) UV-spectra analysis of synthesis process of nanocapsule: AuNPs (a); AuNPs-HRP (b); AuNPs-HRP-PSS (c); AuNPs-HRP-PSS-Ab2 (d). (C) The relationship between the amount of Ab2 and the absorbance value. P/N value is the positive OD value/blank OD value.

Figure 3. Standard curve of nanocapsule probe-based assay for imidacloprid. The curve was obtained by using the relationship between the values of inhibition and the logarithm of the concentrations of imidacloprid. Results are mean ± SD (n = 3).

Table 2. Cross-reactivity (CR) of the probe with imidacloprid and its analogues.

Analogues	Chemical structure	CR^a (%)
Imidacloprid		100.00
Thiacloprid		<10.00
Acetamiprid		<10.00
Clothianidin		<10.00
Imidaclothiz		<1.00
Thiamethoxam		<0.10
Nitenpyram		<0.10
Dinotefuran		<0.10

^aData represent the means of three experiments.

Table 3. Recovery of spiked samples.

Samples	Spiked concentration	Mean recovery^a (%)	CVs (%)
	(μg Kg^−1)	Developed method		Commercial ELISA kit
Rice	2	88.05 ± 7.23	8.21	109.19 ± 7.01	6.42
	10	117.02 ± 8.80	7.52	117.64 ± 1.56	1.33
	20	109.02 ± 10.56	9.69	92.62 ± 1.35	1.45
	0	–^b	–	–	–
Pear	2	89.53 ± 7.11	7.94	90.05 ± 4.96	5.50
	10	96.80 ± 9.78	10.11	95.63 ± 4.13	4.32
	20	109.50 ± 13.73	12.54	83.81 ± 1.45	1.73
	0	–	–	–	–
Cabbage	2	80.34 ± 8.35	10.39	93.50 ± 1.62	1.73
	10	92.55 ± 6.11	6.61	90.08 ± 3.44	3.82
	20	120.84 ± 12.10	10.01	89.22 ± 5.15	5.77
	0	–	–	–	–

^aData represent the means of three experiments.

^bNot detected.

Figure 4. (A) OD₄₅₀ value of assay for the nanocapsule probe stored for different time-periods. (B) The picture of the probe stored at 0 (a), 12 (b) days.

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